The present invention concerns a method for spatially resolving the enlargement and fine adjustment of precious metal nanoparticles according to size on a substrate surface and the nanoparticle arrangements and nanostructured substrate surfaces so produced, and the use thereof.
In recent years, nanostructures and especially ordered structures of precious metal nanoparticles on substrate surfaces have found great interest for a number of applications in different fields. For example, gold nanoparticles can be employed in biochemical sensors (Dyckman and Bogatyrev (2007), Russian Chemical Reviews 76(2), 181-194) and as etching masks to make biomimetic surfaces and interfaces (Lohmüller et al. (2008), NANO LETTERS 8 (5): 1429-1433).
For many of these applications it would be very desirable to adjust the size of these nanoparticles locally and in the nanometer scale on macroscopic substrates with the greatest possible precision. For example, more linker molecules and thus also more desired target molecules could be bound to larger nanoparticles and this capability could be used to produce concentration gradients of a given antigen on a substrate. Thus, e.g., concentration-sensitive biochips could be produced in easy fashion. A fine adjustment of the particle size with high spatial resolution would also be very advantageous for the aforementioned use as etching masks. Such a fine adjustment would make possible, for example, the production of complex nano-optical elements such as Fresnel lenses and zone plates. Ordered areas of precious metal nanoparticles with given diameters could also be used to advantage in new transistors (Sato et al. (1997), American Institute of Physics 82(2), 696-702) or for fluorescence quenching (Fan et al. (2003), PNAS, 100 (1), 6297-6301).
The size of precious metal nanoparticles, especially gold nanoparticles, can basically be adjusted before the deposition on the substrate surface, e.g., by using metal colloids (Kimling et al. (2006), J. Phys. Chem. B., 110, 15700-15707), or after the deposition, e.g., by currentless deposition using a reducing agent (Hrapovic et al. (2007), Langmuir 19:3958-3965). However, in these methods described in the prior art, only a limited size adjustment is possible and most importantly no spatially resolved adjustment of the nanoparticle size.
In German patent application DE 10 2007 017 032 and the corresponding international application PCT/EP2008/0071981 methods are described for the creating of interparticle distance and particle size gradients in gold nanoparticle arrangements that were produced by means of micellar block copolymer nanolithography (BCML). In these methods, particle size gradients are created either by currentless deposition from a solution containing elemental gold, as above, but under variation of the rate at which a substrate surface covered with nanoparticles is pulled out from this solution, or by irradiation with a lateral intensity-modulated light field.
But these methods are not fully satisfactory or suitable for all applications, since it is hard to create several regions with greatly different mean diameters of the nanoparticle and high spatial resolution alongside each other.
A main problem of the present invention was thus to provide improved methods for spatially resolving the enlargement and fine adjustment of precious metal nanoparticles on a substrate surface according to size, by which even very sharp particle size gradients or nanoparticle arrangements containing several regions with greatly differing mean diameters of the nanoparticles and high spatial resolution alongside each other can be produced in an easy and efficient manner. A related problem was to provide the corresponding nanoparticle arrangements and nanostructured substrate surfaces. Yet another problem was to provide the nanoparticle arrangements and nanostructured substrate surfaces produced according to the invention for various applications that thus far were not considered on account of the inadequate or impossible fine adjustment of precious metal nanoparticle arrangements on a substrate surface according to size.
Now, according to the invention, it has been found that the aforementioned main problem can be solved by the method according to the invention, wherein a substrate coated with (preferably fixed) precious metal nanoparticles is contacted with a precious metal salt solution and a localized and controlled enlargement of the nanoparticles in certain given regions is brought about by UV irradiation of these regions. The above-mentioned additional problems are solved by providing the nanoparticle arrangements and nanostructured substrate surfaces and by the use according to the present invention.